The present invention relates generally to stock feeders, and, more particularly, it relates to machines for feeding coils of pre-punched stock into metal-forming equipment such as a stamping or punching press.
A large variety of transfer machines have heretofore been employed for feeding sheet or strip material into forming equipment. Perhaps the simplest involve a pair of feed rolls which engage the stock. Because the stock is smooth and generally oil-coated, however, slippage was a problem, particularly where, as was generally the case, the feed rolls had to provide the power to uncoil the stock and, optionally, pull it through a stock-straightening device.
More recently, machines with travelling edge-grippers have been used. On the forward stroke, the grippers, which may be mechanical, pneumatic or hydraulic, advance the stock a predetermined distance. As the hold of the travelling grippers is relaxed at the end of the stroke, a pair of stationary grippers is actuated which holds the stock during the forming operation, which is co-incident with the return stroke of the travelling grippers. Such machines perform well, but are large, relatively complex and expensive. Such a machine is described in U.S. Pat. No. 3,753,522.
Other prior art feeders are particularly adapted for particular types of stock or to meet particular problems. In U.S. Pat. No. 3,438,557, the grippers are allowed to float laterally, so that camber in the stock will not cause binding in the machine. Vertically floating gripper jaws are disclosed in U.S. Pat. No. 3,735,907, particularly adapted for angle stock, to accommodate bowed (e.g., non-straight) stock.
The availibility of strip stock with precisely-spaced indexing holes makes possible simpler, less expensive and more powerful feeders, as exemplified by the present invention.